1. Field of the Invention
The present invention relates to the treatment of keratinous material, such as attaining permanently waved or straightened hair.
2. The Related Art
Keratin is a major constituent of horns, hoofs, nails and feathers and mammalian hair, such as wool or human hair. Keratin consists of long polypeptide chains crosslinked to one another by cystine disulfide linkages, the crosslinkages conferring structural rigidity on a keratin-containing material.
Permanent hair deformation, i.e. permanent waving and permanent straightening, involves rearrangement of the keratin polypeptide chains.
Hot waving methods employ heat above 140.degree. F., frequently as high as 300.degree. F., and the action of steam and alkali. Hot waving methods have virtually disappeared because they are too complicated and are excessively damaging to the hair. Moreover, hairdressers can not be certain with such methods that the desired results would consistently be obtained. Hot waving, therefore, has gradually been replaced by cold waving.
Permanent hair straightening is sometimes done using a hot metal comb and covering the hair with lipid compounds or an emulsion. More frequently, straightening gels or emulsions containing various proportions of strong bases are used. These permanent hair straightening methods are irritant to the scalp, and careless handling may cause hair damage. Straighteners are sometimes formulated like cold wave products.
In cold permanent waving or straightening, disulfide crosslinkages in hair keratin are ruptured by using various reducing agents. Common reducing agents include inorganic sulfides, sulfites, hydrosulfites, cyanides, mercaptans, thioglycolic acid and various other compounds. Sulfhydryl groups are formed in place of the disulfide linkages. The shaping of the hair into a desired conformation has conventionally been carried out by contacting the hair with a reducing agent in the form of liquids, creams or gels while the hair has been mechanically formed into the desired new shape. The reducing composition is applied to the hair for a sufficient time to allow shaping to occur by the reductive disruption of the disulfide linkages. Finally, disulfide crosslinkages are reformed or novel disulfide linkages are created by applying to the hair oxidizing or crosslinking agents, while maintaining hair in a form which it is desired to render permanent. The final step of establishing disulfide crosslinkages, which may be referred to as the neutralizing or fixing step, is important in order to make the new conformation permanent, to increase tensile strength, to avoid damage to the hair and to remove the sulfhydryl groups as reactive sites.
Oxidative crosslinking employs a number of the usual chemical oxidizing agents or atmospheric oxygen to convert sulfhydryl groups to the corresponding disulfide. Hydrogen peroxide, perborate and bromates have been widely used in permanent hair deformation. Oxidation of sulfhydryl groups with chemical oxidizing agents may be catalyzed by metals. German Patent 1,198,012 discloses the use of small amounts of alkali metal metavanadates, i.e. 0.00025% by weight, to catalyze the bromate-based oxidation of hair.
The oxidative method employing atmospheric oxygen, termed "self-neutralizing", depends on air oxidation to destroy any reducing agent on the hair and to reform disulfide linkages. This method does not necessitate subsequent application of a separate neutralizing solution to the hair; self-neutralizing waving lotions sometimes include metal catalysts in addition to a reducing agent. Den Beste et al., U.S. Pat. No. 2,540,980 and Lang et al., U.S. Pat. No. 4,532,950 disclose addition of manganese chloride or sulfates of cobalt, copper or iron as oxidation catalysts to a waving lotion containing a reducing agent. Wainer, U.S. Pat. No. 2,707,697 discloses incorporation of iron sulfate in a waving lotion containing citric acid. Self-neutralizing waving lotions are poorly suited for professional use or for hair straightening applications and have not gained consumer acceptance.
It is also possible to convert sulfhydryl linkages to disulfide crosslinkages in a non-oxidative manner by using crosslinking agents such as alkylene dihalides or dihalocarboxylic acids as in U.S. Pat. No. 2,739,033 or dimaleimides as in U.S. Pat. No. 2,850,351. Speakman, U.S. Pat. No. 2,261,094 discloses the use in permanent hair waving of polyvalent metals, namely, sulfates of bivalent metals, such as calcium, barium, zinc, copper and nickel. In practice, when bivalent metal sulfates disclosed by the Speakman patent are employed, it has been found desirable to mix such crosslinking reagents with traditional oxidizing agents, such as hydrogen peroxide. The Speakman patent teaches desirability of such mixtures to reduce the time of treatment at col. 4, lines 10-17. Moreover, crosslinkages of bivalent metals with sulfur atoms have been considered ionic and unstable by Patterson et al., J. Res. Nat. Bur. Stand., 27:89. Complexes of dissolved cysteine (reduced cystine) with molybdenum in aqueous solution in the pH range of 4 to 6 have been described by Spence et al., Inorg. Chem., 2 (1963) 319. Spence et al. observed little complex formation above pH 6.5.
Many neutralizing agents which have been proposed heretofore are toxic and thus are difficult to employ. Others are volatile and may be hazardous to use. A crosslinking reagent is desirable that is not encumbered by the difficulties of the past but is as effective as traditional oxidizing treatments.
Therefore, it is an object of the present invention to provide a crosslinking composition for forming disulfide linkages in a keratinous material in which disulfide linkages have been disrupted and replaced by sulfhydryl groups.
It is a further object of the present invention to provide a product for permanent hair waving or straightening comprising a composition for reducing disulfide bonds to form sulfhydryl groups and the aforementioned crosslinking composition.
A still further object of this invention is to provide a method for treating a keratinous material in which disulfide linkages have been ruptured, which method includes contacting the keratinous material with the aforementioned crosslinking composition.
These and other objects will become more apparent by consideration of the detailed description and examples that follow.